CANOGA PERKINS 9175 Configuration Guide - Manual (Page 225)

CanogaOS Configuration Guide
32-2
The queue-rate command in both SAP egress policy and network egress policy controls
the class-level bandwidth limitation. The service-level bandwidth limitation is controlled
by using total-rate command in both egress policies. The EVC can not get more
bandwidth than the configured total rate even if the link is underutilized.
Queue Scheduling
Queue scheduling determines to service which queue at each time instant. The switch
supports SP (Strict Priority) and WDRR (Weighted Deficit Round Robin) scheduling.
In each set of queues of an EVC, each queue is internally associated with a class.
• Queues in different classes are serviced by SP scheduling policy, which means
that queues in the high class will be treated preferentially and queues in the low
class will get opportunity to be served until there are no packets being backlogged
in the high-class queues.
• Queues in the same class will be serviced according to WDRR scheduling policy.
The weight of WDRR scheduling controls the proportion of bandwidth allocation.
WDRR serves queues in the same class according to the weight in a round-robin
manners.
It is not difficult to derive that queues in the class 0 always be treat with the lowest priority
and generally called best-effort queues. Streams destined to these best-effort queues
obtain residual bandwidth proportionally according the weight of WDRR policy.
Congestion Avoidance and WTD Threshold
The service queues use an enhanced version of the tail-drop congestion avoidance
mechanism called WTD. WTD manages the queue lengths and provides drop
precedences for different packet colors. You can configure WTD threshold for service
queues by using the queue <0-3> threshold RED-THRESH YELLOW-THRESH
GREEN-THRESH command in both SAP egress policy and network egress policy.
32.3 Configuration
The configurations for hierarchical QoS generally follow steps below:
• Enabling QoS globally by using qos enable global configuration command.
• Reserving VLAN range for EVC by using ethernet evc reserved start-vlan global
configuration command.
• Creating QoS SAP egress policy by using qos sap-egress global configuration
command, configure queue shaping by using queue-rate QoS SAP-egress policy
command, and configure the group shaping for the service traffic by using
total-rate QoS SAP-egress policy command.
• Creating QoS network egress policy by using qos net-egress global configuration
command, configure queue shaping by using queue-rate QoS network egress
policy command, and configure the group shaping for the service traffic by using
total-rate QoS network egress policy command.
• Creating EVCs by using ethernet evc global configuration command.
• Associating QoS SAP egress policy and network egress policy to an EVC by
using qos-policy sap-egress and qos-policy net-egress EVC configuration
commands, respectively.